After Hurricane Irma's winds took out 90 percent of South Florida's power, many residents wondered why more of the region’s power lines are not underground.

The widespread outage occurred even though the storm brought mostly tropical-force winds instead of hurricane force winds to the region, according to the National Weather Service. Felled trees, flying debris, hurricane wind gusts and some flooding caused most of the damage, according to Florida Power & Light Co.

So what if power lines were underground — and not above ground where poles and lines were knocked out by high winds and fallen trees?

In a post-storm survey of South Florida cities and other communities, the Sun Sentinel found that many are either undertaking or considering burying power lines.

Even FPL, which historically supported overhead construction because it’s easier to fix, says it is now evaluating underground projects in the next phase of “hardening” its electric grid, which powers half the state.

“We will be working on that in the coming months,” said FPL spokesman Chris McGrath, in response to a Sun Sentinel inquiry about recent statements made by James Robo, chairman and CEO of NextEra Energy, the utility company’s parent.

At an investor conference, Robo said that burying more lines was a “potential” part of a corporate plan to harden the system. FPL has spent $3 billion since 2006, and plans to spend another $17 million to $19 million through 2020 to improve reliability, he said.

Robo’s statements followed comments by FPL CEO Eric Silagy, who said that “we’re big fans of undergrounding.”

McGrath said FPL is considering adding more underground power lines because “they provide better reliability day-to-day as well as in storms.” Yet, he warns that underground power lines are generally more expensive and more susceptible to storm surge and flooding, which can result in longer outages.

When Hurricane Irma arrived Sept. 10, it struck a system that Florida Power & Light Co. had spent nearly $3 billion to reinforce....

Some South Florida communities have already installed underground utilities, while others are in the process of undergrounding or are considering it.

“There’s no way it’s going to be worse,” said Keith London, vice mayor of Hallandale Beach, about underground utilities. He pointed to underground utilities becoming the standard in new residential communities. “No one is going to pay hundreds of thousands of dollars for new homes if undergrounding makes it less reliable.”

Boca Raton Mayor Susan Haynie said the loss of power in most older neighborhoods in the eastern part of the city rekindled city council discussions about burying more power lines. New developments downtown are generally required to have underground lines.

Following Hurricane Wilma in 2005, FPL began providing incentives to communities to initiate more undergrounding. Completed projects around South Florida include those in Coconut Creek, Pompano Beach, Sunny Isles, Golden Beach and Jupiter Island, according to an FPL filing with state regulators.

Currently, 40 percent of Florida Power & Light Co.’s distribution system is underground, according to FPL spokesman Bryan Garner. And there are several underground installation projects under way, including one on the island of Palm Beach.

But the burying of lines is expensive. And below-ground networks offer no guarantees of outage-free storms.

It costs an average of $1 million a mile to move main power lines to subterranean levels, according to FPL.

Generally, “underground lines perform better in wind events, but can result in longer outages when they are exposed to flooding,” Garner said. He added that most underground lines connect with above-ground systems at some point, and can still be affected by a storm.

During Irma, communities with underground lines generally fared better, according to interviews with cities, residents and homeowner associations.

In Parkland, all communities west of University Drive have underground power lines, and “they fared quite well during the storm,” said Todd DeAngelis, public information officer for the city. “There were minimal outages and only for short periods, [such as] one day,” he said.

But east of University Drive, where there are largely above-ground utilities, communities “suffered larger scale outages and for longer periods of time,” DeAngelis said.

Weston was built with underground utilities in its major subdivisions. Only Bonaventure doesn’t have underground lines, and it was without power after Irma for several days, residents reported.

Still, FPL said about one-third of its customers in Weston were affected by power outages in Irma, which it is still investigating. “Generally, we are aware that underground-related infrastructure was impacted by Irma, [such as] transformers and underground cables damaged by flooding and uprooted trees,” utility spokesman McGrath said.

Some local communities with underground lines lost power in the storm because they are connected to a power source outside the community that failed in Irma, observers say.

Seven Bridges, a new western Delray Beach community with homes priced from $750,000 to $2.5 million, lost power in Irma. “Our homeowners were wondering what was going on,” said Rick Elsner, vice president of development for builder GL Homes.

While it’s hard to get to the bottom of it, but he believes that at Seven Bridges, “there was a [downed] transmission line somewhere off our property.”

Transmission lines are what moves the power from a plant to a substation. So when transmission is affected, underground distribution lines aren’t receiving power.

“I love underground power lines — they do present a more stable power system. But they’re only as good as what comes next to it,” Elsner said.

Even within many neighborhoods, there can be a mix of underground and overhead equipment. When there’s a storm, one resident may be without power while a neighbor never loses it.

Housing analyst Jack McCabe points to his Deer Creek Golf Club neighborhood, which has underground lines in the newer part including his home. “I never lost power. But the section that’s older, they were out for about eight days -- that’s fairly representative,” McCabe said.

But some cities believe that slowly converting their electric grids to those with underground lines will make a difference in overall resiliency.

Hollywood began the conversion to underground on its beachfront in 1997, part of an improvement and beautification strategy. Underground lines have been completed on 22 streets, and the city is in the process of installing lines underground on 13 additional streets. Another 18 streets are scheduled to receive them.

There were some power outages in Irma, but overall storm-related power outages have been fewer, the city said. Hollywood attributes that to the fact that there are no overhead lines that can be damaged by downed trees.

Hollywood beach property owners pay no additional taxes for burying power lines. A portion of their regular taxes is retained for the community redevelopment agency, in a long-ago deal to improve what was a blighted area.

“I don’t think there’s any question the conditions on the beach, should be fortified once this said all and done,” said Jorge Camejo, executive director of Hollywood’s CRA.

In Fort Lauderdale, several older neighborhoods have installed or are in the process of getting underground lines. Nurmi Isles already has underground lines, while ldlewyld, Riviera Isles, Las Olas Isles, Seven Isles, Harbor Beach and Sunrise Key have submitted applications to begin the undergrounding process, according to Chaz Adams, public affairs manager for the city.

Seventy percent of residents in those neighborhoods, where homes are worth millions of dollars, have to approve the conversion project, which would be paid for through special property assessments over 10 to 30 years.

Another wealthy enclave, Palm Beach, began the first phase of the all-island conversion of overhead to underground utilities this summer. The project will cost a total of $98.6 million, paid for through a special annual assessment of $1,191 homeowners and $331 for condominiums, according to Thomas Bradshaw, deputy mayor. He has been working since 2003 for undergrounding approvals.

President Trump’s Mar-A-Lago estate, for example, will be required to make a one-time payment of $449,564, or pay $28,870 a year for 30 years.

Underground installation on Palm Beach was approved in 2014, after FPL said it planned to “harden” the island’s power poles. That meant “ugly commercial poles” made of concrete or steel, which residents didn’t want for aesthetics’ sake, Bradshaw said. But a change was needed: Palm Beach also has been experiencing more frequent power outages and even fires from sparking power lines and broken transformers, he said.

The handful of communities on the island that already have installed underground lines did lose power in Irma. But it is for a shorter time, and “they didn’t have the broken poles and tangled wires,” Bradshaw said.

Besides putting the island’s utilities underground, FPL plans to harden the main feeder lines to substations, located across the Intracoastal Waterway in West Palm Beach. “At end of the day [Palm Beach is] going to have the maximum reliability you can,” he said.

Palm Beach’s Bradshaw said he recognizes that underground power lines may not be affordable for a lot of South Florida communities.

But he has this bit of advice: “It’s always cheaper today than it will be tomorrow. If it’s something they think they want, it’s easier to bite the bullet now than in the future.”